Process for the preparation of toluenediamines by catalytic hydrogenation of dinitrotoluenes

Abstract

The present invention relates to a process for the preparation of toluenediamine, in which dinitrotoluene is reacted with hydrogen in the presence of a catalyst. The dinitrotoluene required by this process has a content of carbon dioxide, in either physically dissolved or chemically bonded form, of not more than 0.175 mol %, based on the molar amount of the dinitrotoluene.

1. A process for the preparation of toluenediamine comprising reacting dinitrotoluene with hydrogen in the presence of a catalyst, wherein said dinitrotoluene has a content of carbon dioxide in physically dissolved form or chemically bonded form of less than 0.175 mol %, based on the molar amount of dinitrotoluene. 
     
     
       2. A process for the preparation of toluenediamine, comprising:
 a) reacting toluene with nitrating acid to form a reaction mixture comprising mononitrotoluenes, 
 b) separating said reaction mixture comprising mononitrotoluenes into an organic phase comprising mononitrotoluenes and an aqueous phase comprising sulfuric acid, 
 c) reacting said the organic phase comprising mononitrotoluenes with nitrating acid, to yield a reaction mixture comprising an isomeric mixture of dinitrotoluenes, 
 d) separating said reaction mixture comprising an isomeric mixture of dinitrotoluenes into an organic phase comprising dinitrotoluenes and an aqueous phase comprising sulfuric acid, 
 e) purifying said organic phase comprising dinitrotoluenes with water, in a multi-stage extraction in which each stage comprises mixing and phase separation, to yield an isomeric mixture of dinitrotoluenes comprising (i) from 74 to 81% by weight of 2,4-dinitrotoluene, (ii) from 17 to 21% by weight of 2,6-dinitrotoluene, and (iii) less than 5.5% by weight of the 2,3-isomer, the 2,5-isomer, the 3,4-isomer and the 3,5-isomer of dinitrotoluene, with the sum of (i), (ii) and (iii) totalling 100% by weight of dinitrotoluene, 
 f) reacting said isomeric mixture of dinitrotoluenes with hydrogen, in the presence of a catalyst to form toluenediamines, 
 
       wherein
 (1) the dwell time for the mixing in each stage of the multi-stage extraction in step e) is at least 4 minutes and not more than 60 minutes, 
 
       and
 (2) an inert gas is additionally introduced into the mixture of the organic phase comprising dinitrotoluenes and water in at least the last stage of the extraction in step e), with the weight ratio of inert gas to dinitrotoluenes being such that the resultant purified isomeric mixture of dinitrotoluenes have a total content of carbon dioxide in physically dissolved or chemically bonded form of less than 0.175 mol %, based on the molar amount of the dinitrotoluenes. 
 
     
     
       3. The process of  claim 2 , wherein in e) said purifying step, alkaline water is present in at least one stage of the multi-stage extraction and neutral water is present in at least one stage of the multi-stage extraction. 
     
     
       4. The process of  claim 1 , wherein said catalyst comprises at least one nickel-containing catalyst. 
     
     
       5. The process of  claim 2 , wherein said catalyst comprises at least one nickel-containing catalyst.